This operation allows you to update the source of the ordering of
product relation definitions. This is relevant when a product has multiple relation definitions added to it and
one wants to control the exact ordering of them. Either the relation definitions are sorted by the order they
are in the general list of relation definitions, or they are sorted in the order they are in the current
product identified by id. For example: If a product has two relation definitions added to it like:
- "Contains"
- "Spare part of"
The order to use when listing these two relation definitions can be set to follow either the
ordering in the general list of relation definitions (source = RELATION_DEFINITION) or the ordering in the
list of relation definitions stored on the product itself (source = PRODUCT).